1. Field of the Invention
The present invention relates to a method for assembling a rotor with permanent magnets, a holder applied thereby, and a rotor obtained by such a method.
2. Related Art
More specifically, the invention is intended for assembling such a rotor for use in interior permanent magnet motors (IPM).
In standard induction motors the rotor is composed of ferromagnetic lamellae, which are held together by a cage, usually made by injection moulding.
Motors with a laminated rotor are also known, whereby permanent magnets are positioned in ferromagnetic lamellae, and which motors, as result thereof, do not have a cage and require another way of compressing and holding the lamellae together.
It is known that when assembling this last type of motor the lamellae are first joined together in a stack and are mutually attached, for which different methods are already known.
For instance, it is possible to punch the lamellae to each other, or even to attach them to each other by means of rivets or welded joints.
A disadvantage of this method is that the local connections between the isolated lamellae result in a reduced performance of the motor, since they have a negative influence on the iron losses induced by the magnetic field.
A possible solution is the use of adhesives to connect these lamellae to each other. A disadvantage is that when sticking the lamellae together by means of adhesives, this method is expensive and sensitive to temperature.
Another disadvantage is that it is difficult to introduce the permanent magnets in recesses provided for this purpose in the lamellae that are already joined together. The permanent magnets exert high forces on the ferromagnetic lamellae and on the other magnets already positioned in place as a result of which they do not remain automatically on their position.
Another disadvantage of the lamellae that have already been joined is the possibility to make mistakes by mounting the magnets in an incorrect orientation in the recesses provided for this purpose, more specifically with the north-south direction of the magnets opposite to the intended north-south direction.
It is known that this incorrect orientation can be avoided by mounting the magnets in non-magnetised state in the rotor and magnetize them afterwards, together with the whole rotor, but this way of magnetising has the disadvantage of involving a high energy requirement.